two-bit/minecraft-machine.test.ts

import { minecraftMachine } from "./minecraft-machine"
import { ram } from "./ram"
import { Word, wordFromNumber, wordFromString } from "./word"

const push = wordFromString("00") as Word<2>
const jump = wordFromString("01") as Word<2>
const add = wordFromString("10") as Word<2>
const write = wordFromString("11") as Word<2>
const any = wordFromString("00") as Word<2>

describe("Minecraft machine", () => {
    let subject: ReturnType<typeof minecraftMachine>

    beforeEach(() => {
        const bank1Ram = toWordArray([
            "1011",
            "0001",
            "0000",
            "1110"
        ])

        const bank2Ram = toWordArray([
            "1111",
            "0101",
            "1010",
            "1000",
            "0011"
        ])

        const instructions = [
            "0000"
        ].map(value => wordFromString(value) as Word<4>)

        subject = minecraftMachine(bank1Ram, bank2Ram, instructions)
    })

    test("starts with the program counter pointing at 0x0", () => {
        expect(subject.programCounter.value().toString()).toEqual("0000")
    })

    test("starts with the address register pointing at 0x2", () => {
        expect(subject.addressRegister.value().toString()).toEqual("0010")  
    })

    test("starts with the extended address register pointing at the first memory bank", () => {
        expect(subject.extendedAddressRegister.value().toString()).toEqual("0000")
    })

    test("starts with an empty stack", () => {
        expect(subject.stack.values().map(word => word.toString())).toEqual(["0000", "0000", "0000", "0000"])
    })

    test("loads the first ram bank with the provided values starting after reserved addresses, leaving unspecified values as zeros", () => {
        expect(wordsToStrings(subject.bank1Ram.values())).toEqual([
            "0010", "0000", "1011", "0001",
            "0000", "1110", "0000", "0000",
            "0000", "0000", "0000", "0000",
            "0000", "0000", "0000", "0000"
        ])
    })

    test("loads the second ram bank with the provided values starting after reserved addresses, leaving unspecified values as zeros", () => {
        expect(wordsToStrings(subject.bank2Ram.values())).toEqual([
            "0010", "0000", "0000", "0000",
            "0000", "1111", "0101", "1010",
            "1000", "0011", "0000", "0000",
            "0000", "0000", "0000", "0000"
        ])
    })

    describe("push instruction", () => {
        beforeEach(() => {
            subject = minecraftMachine(toWordArray(["1101", "0110"]), toWordArray(["1010"]), [push.concat(push)])
            subject.addressRegister.set(wordFromString("0010") as Word<4>)
        })

        test("loads value at address register onto the stack", () => {
            subject.tick()

            expect(wordsToStrings(subject.stack.values())).toEqual(["1101", "0000", "0000", "0000"])
        })

        test("increments the stack pointer", () => {
            subject.tick()

            expect(subject.stackPointer.value().toString()).toEqual("01")
        })

        test("loads the value on top of the existing stack", () => {
            subject.tick()
            subject.tick()

            expect(wordsToStrings(subject.stack.values())).toEqual(["1101", "0110", "0000", "0000"])
        })
        
        test("increments the address register", () => {
            subject.tick()

            expect(subject.addressRegister.value().toString()).toEqual("0011")
        })

        test("loads value from bank 2 if extended address register is pointing there", () => {
            subject.extendedAddressRegister.set(wordFromNumber(1, 4) as Word<4>)
            subject.addressRegister.set(wordFromString("0101") as Word<4>)

            subject.tick()

            expect(wordsToStrings(subject.stack.values())).toEqual(["1010", "0000", "0000", "0000"])
        })

        test("does not increment the stack pointer if the stack is full", () => {
            subject.stackPointer.set(wordFromString("11"))

            subject.tick()

            expect(subject.stackPointer.value().toString()).toEqual("11")
        })

        testIncrementsTheProgramCounter(() => subject)
    })

    describe("jump instruction", () => {
        beforeEach(() => {
            subject = minecraftMachine(toWordArray([]), toWordArray([]), [jump.concat(any)])
            subject.stackPointer.set(wordFromString("01"))
        })

        describe("when the previous stack value is greater than zero", () => {

            beforeEach(() => {
                subject.stack.write(wordFromString("0001") as Word<4>, wordFromString("00"))
                subject.stack.write(wordFromString("0100") as Word<4>, wordFromString("01"))

                subject.tick()
            })

            test("sets the program counter to the current stack value", () => {
                expect(subject.programCounter.value().toString()).toEqual("0100")
            })

            test("resets the instruction pointer", () => {
                expect(subject.instructionPointer.value().toString()).toEqual("0")
            })

            test("pops the current value", () => {
                expect(subject.stackPointer.value().toString()).toEqual("00")
            })
        })


        describe("when the previous stack value is zero", () => {
            test("pops the current value", () => {
                    
            })

            testIncrementsTheProgramCounter(() => subject)
        })
    })
})

function testIncrementsTheProgramCounter(getSubject: () => ReturnType<typeof minecraftMachine>) {

    let subject: ReturnType<typeof minecraftMachine>

    beforeEach(() => {
        subject = getSubject()
    })
    
    test("does not increment the program counter if the current instruction is the first", () => {
        subject.tick()

        expect(subject.programCounter.value().toString()).toEqual("0000")
    })

    test("increments the program counter if the current instruction is the second", () => {
        subject.tick()
        subject.tick()

        expect(subject.programCounter.value().toString()).toEqual("0001")
    })

    test("toggles the instruction pointer", () => {
        subject.tick()

        expect(subject.instructionPointer.value().toString()).toEqual("1")

        subject.tick()

        expect(subject.instructionPointer.value().toString()).toEqual("0")
    })
}

function toWordArray(values: string[]) {
    return values.map(wordFromString) as Word<4>[]
}

function wordsToStrings(values: Word<number>[]) {
    return values.map(value => value.toString())
}